In one of the most ambitious attempts yet to thwart Alzheimer's disease, a major study got under way Monday to see if an experimental drug can protect healthy seniors whose brains harbor silent signs that they're at risk.

Scientists plan to eventually scan the brains of thousands of older volunteers in the U.S., Canada and Australia to find those with a sticky build-up believed to play a key role in development of Alzheimer's - the first time so many people without memory problems get the chance to learn the potentially troubling news.

Having lots of that gunky protein called beta-amyloid doesn't guarantee someone will get sick. But the big question: Could intervening so early make a difference for those who do?

Researchers are just beginning to recruit volunteers, and on Monday, a Rhode Island man was hooked up for an IV infusion at Butler Hospital in Providence, the first treated.

Peter Bristol, 70, of Wakefield, R.I., figured he was at risk because his mother died of Alzheimer's and his brother has it.

"I felt I needed to be proactive in seeking whatever therapies might be available for myself in the coming years," said Bristol, who said he was prepared when a PET scan of his brain showed he harbored enough amyloid to qualify for the research.

"Just because I have it doesn't mean I'm going to get Alzheimer's," he stressed. But Bristol and his wife are "going into the situation with our eyes wide open."

He won't know until the end of what is called the A4 Study - it stands for Anti-Amyloid Treatment in Asymptomatic Alzheimer's - whether he received monthly infusions of the experimental medicine, Eli Lilly & Co.'s solanezumab, or a dummy drug.

Solanezumab is designed to help catch amyloid before it builds into the brain plaques that are a hallmark of Alzheimer's. It failed in earlier studies to treat full-blown Alzheimer's - but it did appear to help slow mental decline in patients with mild disease, raising interest in testing it even earlier.